a) Field of the Invention
This invention relates to a tube-pressed brake band suitable for use in an automatic transmission, brake or the like.
b) Description of the Related Art
As will be described next, binding means for conventional brake bands include those for pressing a bracket attached to one end of a strap and those for applying a pressure by a tube itself without using such a strap.
FIG. 7 shows a conventional brake band 50 of the bracket type, which is provided with a strap 51, an apply-side bracket 52, a piston 53 for pressing the apply-side bracket 52, an anchor-side bracket 54, and a friction material 55 bonded on an inner wall of the strap 51. Designated at numeral 56 is a counterpart inner member to be bound by the brake band 50.
In the brake band of this type, force tends to be applied locally to the brackets so that the brackets may develop cracks. The brake band of this type is accompanied by an inconvenience that any attempt to enhance the strength of the brackets leads to an increase in manufacturing cost.
FIG. 8 is a cross-sectional view of a conventional brake band 60 of the tube type, and FIG. 9 is a cross-sectional view of the conventional brake band 60 as taken along a line IX-O of FIG. 8. The brake band 60 of the tube type is provided with an outer frame 61, a ring-shaped tube 62, a friction material 63 bonded on an inner peripheral surface of the tube 62, and a hole 64 for feeding a pressure fluid into the tube 62. Designated at numeral 65 is a void space where an unillustrated inner member is accommodated as a counterpart.
By injecting or releasing a pressure fluid, for example, a gas such as compressed air or a liquid such as pressure oil into or from the tube 62 through the pressure fluid feed hole 64, the tube 62 is inflated or deflated to apply or release pressure. In conventional brake bands of the tube type, tubes are required to have substantial strength as torques are borne by the tubes themselves. Each tube must therefore be provided with a significant thickness, leading to an inconvenience in that the brake band cannot avoid a dimensional increase.
Incidentally, reference is had to FIG. 9. The torque capacity T of a brake band of the tube type is expressed by the following formula: EQU T=2.pi..mu..multidot.R.sub.p .multidot.R.sub.f .multidot.B.multidot.P
where
.mu.: coefficient of friction PA1 R.sub.p : pressure-receiving radius PA1 R.sub.f : radius of friction surface PA1 B: pressure-receiving width PA1 P: pressure applied to the tube PA1 a strap arranged between the counterpart and the tube and relative to an angular direction, fixed at an end thereof on the other one of the inner and outer rings.